This invention relates to an actuation and control system for applying the brakes on a towed vehicle by commands from and/or in response to the operation of the towing vehicle, in particular, in response to actuation of the brakes on the towing vehicle. In a more particular sense, the invention relates to an apparatus for remotely applying and controlling the brakes on a towed automobile or the like, such as typically is equipped with a hydraulic brake system that operates in response to brake pedal movement by the driver, for which remote actuation and control is a highly desirable feature when the automobile is being towed by another vehicle, for example, a motorhome or other recreational vehicle.
As is often observed in highway travel, recreational vehicle users such as motorhome operators frequently tow an automobile behind the recreational vehicle in order to have more convenient transportation when the recreational vehicle is parked at some camping site or park. This is particularly desirable when the recreational vehicle is large and inconvenient for short trips such as shopping or sightseeing, or when it is parked and connected to various utilities whose disconnection is inconvenient, as is usually the case.
When automobiles are so towed on the highway, operation of their brakes from or in correspondence to those of the towing vehicle is usually not attempted since an effective means for doing so has historically not been available, or not convenient to install or use. At the same time, most automobiles possess considerable size and mass, and thus impose an undue additional burden on the braking system of the towing vehicle, for which the latter is in most instances not initially designed. Thus, the desirability of utilizing the existing onboard braking system of a towed automobile has been generally recognized for some time, but since automotive braking systems are closed hydraulic systems and it is undesirable as well as potentially hazardous to open them and connect extraneous devices in flow communication with them, and since most modern automobiles employ power brakes of one type or another which only operate effectively while the vehicle engine is running, the problem is a difficult one which has not as yet been satisfactorily solved.
In an effort to solve the problem identified above, a number of different products have been put on the market or proposed for actuating the brake pedal on the towed vehicle in response to some command from the towing vehicle, such as by using a manual control switch or deriving a signal from the brake light excitation voltage present when the towing vehicle brakes are applied, together with some electrical, mechanical, hydraulic, or pneumatic means for moving the brake pedal on the towed vehicle by pushing or pulling it. In most such cases, the towed vehicle brakes are not applied in a manner proportional to the operation of the towing vehicle brakes, and this creates a disparity in braking force between the two vehicles. Some such systems do achieve a limited amount or an approximation of braking proportionality, in some cases by actually tapping into thc otherwise-closed hydraulic system of the towing vehicle and using the varying hydraulic pressure as a proportional signal or force, and sometimes by monitoring towing vehicle brake pedal movement. These systems usually require some form of additional hydraulic cylinder to be installed on the towed vehicle braking system (i.e., a slave cylinder coupled to the master cylinder of the towed vehicle), and this not only requires the use of expensive additional parts but also requires a licensed mechanic to do the installation. In addition to these disadvantages, these approaches inevitably create a risk of brake failure on either or both the towing vehicle and towed vehicle.
A different and non-intrusive towed vehicle braking system is a modification of the well-known xe2x80x9csurge systemsxe2x80x9d, in which the hitch mechanism between the towed vehicle and the towing vehicles allows for a limited range of relative motion between the two vehicles in response to speed changes that occur during braking, i.e. they allow the towed vehicle to move forward relative to the towing vehicle when the brakes of the latter are actuated, and this change in relative position is coupled mechanically or hydraulically to the foot pedal or master cylinder actuation linkage of the towed vehicle, such that the brake pedal and/or master cylinder piston of the towed vehicle is moved so as to apply the brakes on the towed vehicle. While there are a number of significant limitations and/or disadvantages in the use of such systems, they do at least provide a form of proportional braking for the towed vehicle based on the braking of the towing vehicle.
Other proposed braking systems for this purpose utilize large and cumbersome mechanisms that are bolted onto the floor of the towed vehicle, or wherever else space permits, whenever it is to be towed, to operate the brake pedal by means of levers, solenoid plungers, or power cylinders attached to the brake pedal; however, these systems do not actually achieve true proportioning operation of the towed vehicle brakes since the length of actuator travel does not in fact equate to proportional braking force. On the contrary, such proportionality must come from the difference in pressure introduced into the braking system of the towed vehicle as a result of force exerted on the brake pedal or master cylinder piston.
In one aspect, the present invention provides a simple but highly effective system and apparatus for achieving proportional braking of a towed vehicle based on the braking operation of the towing vehicle, and the invention achieves this desirable result without any intrusion into the hydraulic system of either vehicle, as well as with minimal and easy modification of the towed vehicle. Further, the invention achieves these desirable results by taking advantage of the power braking system in the towed vehicle without operating the vehicle engine, thereby providing truly effective braking in an economical and reliable manner.
In another aspect, the invention provides apparatus for controllably operating hydraulically actuated brakes on the towed vehicle in response to the motion of a towing vehicle, including a control unit having a sensor which provides an electrical output signal in response to deceleration of the towing vehicle, and the brake actuation assembly having an electrical input coupled to receive the electrical output signal from the control unit and having a mechanical output member which is controllably moved in accordance with the electrical output signal from the control unit, the hydraulically actuated brakes of the towed vehicle including a movable operating member onboard the towed vehicle for controllably operating its hydraulic brakes and the mechanical output member of the brake actuation assembly being connectable to the movable brake-operating member of the towed vehicle to operate its hydraulic brakes and slow the towed vehicle in response to sensed deceleration of the towing vehicle. In a particular example, the movable brake-operating member on board the towed vehicle would be a brake pedal normally operable by the driver of the vehicle, and in a preferred embodiment the mechanical output member of the brake actuation assembly comprises or includes a flexible cable which pulls on the brake pedal rather than pushing it.
In other aspects of the invention, in particular preferred embodiments, the brake actuation assembly includes a switchable or otherwise controllable clutch, in particular a slip clutch, preferably an electromagnetic clutch. In other particular or preferred aspects, the control unit may be implemented by use of conventionally available electrical trailer brake controllers, preferably but not necessarily of the type which include an inertia sensor and provide an output brake-actuation signal which is proportional to the sensed deceleration of the towing vehicle.
The foregoing principal aspects and features of the invention will become better understood upon review of the ensuing specification and the attached drawings, describing and illustrating preferred embodiments of the invention.